a) Field of the Invention
This invention relates to a polyphenylene ether resin composition which, while retaining the inherent high heat distortion point of polyphenylene ether resin, is excellent in formability such as moldability and extrudability (hereinafter collectively called "moldability"), does not give off an unpleasant offensive odor in the course of production thereof and can form injection-molded articles free of silver streaks.
b) Description of the Related Art
Polyphenylene ether resin is considered to be highly attractive as an extremely useful engineering plastic for its electrical and mechanical properties, high heat distortion temperature and self-extinguishing properties. Due to its high melting point and high melt viscosity, however, polyphenylene ether resin requires high temperature and pressure upon molding or processing, thereby making its melt molding or processing difficult. As a method for improving the moldability and processability of polyphenylene ether resin, it has been attempted to blend one or more other resins. Blending of a polystyrene resin is widely known. For example, Japanese Patent Publication No. 19812/1968 discloses a polyphenylene ether resin which composes a blend of polyphenylene ether resin and a high-impact polystyrene resin. This composition is widely known in the name of "Noryl" (trade mark; product of General Electric Company). Although it has improved moldability, processability and impact strength, the moldability and processability are still insufficient. Moreover, a substantial drop is observed in heat distortion temperature as a result of the blending.
As another method for improving polyphenylene ether resin, it has been investigated to add a plasticizer to polyphenylene ether resin. For example, Japanese Patent Publication No. 5220/1984 indicates that improved moldability and processability are available by blending a compound, which has good compatibility with polyphenylene ether resin and is selected from aromatic organic acid esters, aromatic-group-containing polyesters, aromatic-group-containing organophosphoric acid esters and chlorinated aromatic hydrocarbons, with a composition of polyphenylene ether resin and a polystyrene resin. This method is however accompanied by the problem that thermal performance of polyphenylene ether resin, such as the heat distortion temperature, is substantially lowered by the blending of the plasticizer although the moldability and processability are improved.
Japanese Patent Laid-Open Application No. 110454/1975 discloses inter alia addition of a low molecular-weight polystyrene to polyphenylene ether resin. Although the addition of such a low molecular weight polystyrene can improve the moldability and processability to some extent, unpleasant offensive odor occurs in the course of its production in which the polyphenylene ether resin and the low molecular weight polystyrene are molten and kneaded and then pelletized so that long-term work is difficult. Presumably, as the resins are molten and kneaded at a temperature as high as 250.degree. C. or higher, the low molecular polystyrene undergoes thermal decomposition, thereby producing gas such as styrene oligomers. Further, many silver streaks are observed in injection-molded products so that their values as commercial products may be impaired in certain instances. The utility of polyphenylene ether resin is recently spreading to the electric and electronic fields. Prevention of static electrification is required in some instances so that conductive carbon may be added. Conductive carbon however substantially reduces the fluidity and, even when low molecular weight polystyrene is added, injection molding at a temperature as high as 300.degree. C. or higher is needed. In addition, many silver streaks occur so that no satisfactory molded product can be obtained. Further, because polyphenylene ether resin and low molecular weight polystyrene are fully compatible with each other, the heat distortion temperature drops in proportion with the amount of the low molecular weight polystyrene added.
U.S. Pat. No. 4,826,919 discloses inter alia addition of low molecular weight polystyrene and an .alpha.-methylstyrene copolymer to a composition of polyphenylene ether resin and a polystyrene resin. Although the drop in heat distortion temperature is small and the moldability and processability are improved to a certain extent, unpleasant offensive odor is given off during the pelletization step and the resulting injection molded product presents many silver streaks, thereby substantially impairing its value.
As is understood from the foregoing, in the field of polyphenylene ether resin compositions, no composition has been obtained yet with excellent balance between heat distortion temperature and moldability and processability and without giving off unpleasant offensive odor upon production or showing poor moldability.